The present invention relates to a current mirror circuit which is able to has a wide range of output voltage.
In a current mirror circuit, the magnitude of output impedance is one of extremely important matters that need to be taken into consideration.
In a conventional simple current mirror circuit as shown in FIG. 81, the output impedance can not be increased so as to be greater than the output impedance of a transistor. In order to improve this, a cascode constitution has been used as shown in FIG. 82. However, there is a problem in that this constitution is not suitably operated when the output voltage is not greater than approximately VT+VDS(sat).
In order to solve this problem, there is a method for selecting a bias of T4 for connection to a cascode as shown in FIG. 83. However, in this constitution, two systems of the same currents are required, and the suitable values of T4 for the channel width/channel length of T3 which forms a gate bias of T4 disperses in the manufacturing process, so that it is difficult to design this constitution. In addition, FIG. 84 illustrates another conventional circuit wherein Vbis is selected to be approximately VDS(sat) to increase an output impedance so as to be suitably operated at an output voltage greater than approximately 2VDS(sat).
However, there is a problem in that it is not possible to accurately replicate a current since the drain-to-source voltage of T1 is different from that of T2. In addition, in order to equalize the drain-to-source voltages of T1 and T2 to enhance the accuracy of the replicated current, there is proposed a method for using two sets of operational amplifier circuits as shown in FIG. 85. However, in this method, there is a new problem in that the scale of circuit is increased.
Thus, in conventional current mirror circuits, there are problems in that in the case of the simple circuit, it is not possible to increase the accuracy of the replicated current, and in the case of the circuit for enhancing the accuracy of the output impedance and the replicated current, the scale thereof is increased.